Oxalacetate

Oxalacetate is a four-carbon dicarboxylic acid that plays a crucial role in cellular metabolism. Its chemical formula is C4H4O5. Oxalacetate is a key intermediate in several metabolic pathways, most notably the citric acid cycle (also known as the Krebs cycle or TCA cycle) and gluconeogenesis.

In the citric acid cycle, oxalacetate is regenerated at the end of the cycle by the oxidation of malate, and it then condenses with acetyl-CoA to begin the cycle anew. This reaction, catalyzed by citrate synthase, forms citrate. Oxalacetate's constant presence is vital for the continuous operation of the citric acid cycle, which is the primary source of ATP (adenosine triphosphate), the energy currency of cells, in aerobic respiration.

Beyond its role in energy production, oxalacetate is also a precursor for the synthesis of glucose during gluconeogenesis, a process that occurs primarily in the liver and kidneys to maintain blood glucose levels. It can also be decarboxylated to form pyruvate or converted to aspartate in the transamination reaction. Furthermore, oxalacetate is involved in the anaplerotic reactions, which replenish intermediates of the citric acid cycle. Its synthesis can occur through the carboxylation of pyruvate. The balance of oxalacetate levels is tightly regulated to ensure metabolic homeostasis.